Acrylic tank is developing a hazy/opaque film

[merk]

I have an acrylic tank that has started to develop a haze appearance. It doesn’t look like scratches and all the water quality are with normal ranges. With some elbow grease and magic eraser it comes off but I was wondering if anyone has any idea what could be causing it?
I have another acrylic reef aquarium that doesn’t have this problem.

 

[blaxsun]

I guess clean off as much of the affected areas as you can and see if it returns. It could just be algae? I use vibrant on my tank every 1-2 weeks and it seems to keep a lot of that at bay.

 

[Sshannon]

Have you dosed any phosphate removers with lanthanum chloride in them?